1. Field of the Invention
The present invention relates to destructive distillation apparatus. More particularly, the present invention relates to discharge systems for apparatus useful in the destructive distillation of waste automobile tires.
2. Discussion of the Prior Art
In the destructive distillation of carbonaceous materials, such as bulk chips of used automobile tires, the finely divided, disperse solids product or residue must be removed from the distillation apparatus. In the case of a batch still the removal of solids material is laborious and time consuming and results in significant downtime for the still. A continuously operating still is clearly desirable to carry out the destructive distillation process in an efficient manner with minimum labor. The lack of an effective system for the safe removal of hot solids material from a continuous destructive distillation apparatus has remained a substantial impediment to the use of continuous stills due to the difficulties involved in handling a continuous stream of finely divided, disperse solids product while preventing either the flow of distillation product gas or vapors out of the system with the carbonaceous solids, which can result in a fire, once the materials reach the outside atmosphere, or the flow of atmospheric air back into the still resulting in fires and explosions. Explosions result in equipment damage and process downtime.
Various systems have been employed in prior discharge systems to avoid potential explosions, including inert gas generators to blanket the discharge system with an inert gas such as combustion gas or nitrogen, and the use of lock hoppers or drop hoppers to isolate the discharge system from ambient air. The provision of inert gas generators in the system adds cost and complexity, and they are subject to failure, resulting in explosion hazards. Lock hoppers or drop hoppers, which provide an air lock between sequentially operated flap valves or rotating vane valves to provide for removal of disperse solids, are less than totally effective in excluding ambient air from the system and are ineffective in preventing the exit of product gases from the distillation process. Rotating vane valves are subject to excessive wear in the hot solids environment contemplated by the invention and fail to effect an adequate seal. Material buildup on flaps or gates results in unacceptable leakage of air and product gases.
The above-described drawbacks of prior art discharge systems have been overcome by the discharge system of the present invention wherein the discharge solids act as a plug seal to avoid the unwanted flow of product gas or ambient air therethrough while effectively discharging finely divided, disperse solids material from a continuously operating distillation apparatus. The use of positive displacement augers having close clearance between the auger and auger cylinder wall, combined with an open section within the auger cylinder where a material plug forms, results in improved sealing of the inventive system from unwanted transfer of gases.
The formation of a solids material plug for sealing in feeding systems is employed by Taylor (U.S. Pat. No. 4,225,392) for gasifier apparatus. However, it has not been previously recognized that the hot, disperse, and finely divided solids exiting a distillation apparatus, such as carbon black formed from the distillation of automobile tire chips, would be effective in the formation of a sealing plug. Although the solid material sealing plug feature of the present invention is primarily intended as an additional sealing feature useful in conjunction with conventional drop or lock hoppers, it is envisioned that in some circumstances the use of these additional mechanical systems could be eliminated when using the sealing plug technology of the present invention. Also, the provision of inert gas systems as part of the discharge system may be eliminated by the employment of the inventive sealing plug system.
It also is generally known to use inclined auger conveyors in combination with valved lock hoppers in a solids discharge system for a retort or still, as shown, for example, by Everman et al. (U.S. Pat. No. 4,690,732. However, the improvements of the present invention, i.e., the provision of a sealing plug section within the auger conveyor apparatus, along with the provision of small clearances between the outer edge of the auger flight and the auger cylindrical casing, allows the continuous operation of the distillation system without unwanted passage of ambient air into the system, or the passage of distillation product gasses through the discharge system, and inhibiting the passage of gas surges from the distillation apparatus through the auger conveyor to the solids disposition area.